A/C Compressor Cycling... E55
 

Need some advice please.

A/C was cool but felt it needed a bit of a boost. Added some R134a and everything seemed to be working fine and was blowing cooler.

Next morning A/C was working great and freezing me out of the car. Ambient temperature about 70 but humid. Didn't drive car at lunch and on drive home, couldn't get the a/c to stay on. Ambient temperature about 92 (probably 95-100 on road). When I got home, checked compressor and it would come on for about 2 seconds and then cut off every 10 seconds or so. I checked the Climate Control "hidden menu" and the compressor pressure (value 7) was at 25 and would rise to 32 as the compressor kicked on but then dropped back down to 25. After about an hour of driving (and about 2 minutes from home), it started to work fine.

Did I put possibly put too much R134 in? When I put the cheap attached pressure gauge on the low side, it showed 80-90 psi when the compressor was off and then dropped down to 40 when the compressor came on. I know from reading other posts the low pressure reading doesn't really mean much by itself.

Thanks in advance for any help.

Kevin
Atlanta
2000 E55

It's overcharged. The CC panel reading confirms it. The cycling is the high side pressure causing the compressor to switch off.

Sounds overcharged to me too.

Either you have too much refrigerant or your pressure sending unit is defective. I'd bet on the former also.

If you put the can in a pan of ice and water, you can draw some refrigerant out of the system without venting any more than it takes to connect the hose. Don't run the compressor while doing this.

Thank you. I'll see if I can get reduce the amount of pressure in the system. May have to take it to my neighbors Benz shop.

Regards,
Kevin

You should take the car to a shop that has R134a recovery equipment. Have them recover the refrigerant and then re-charge with the correct amount of refrigerant.

An overcharged system is very hard on the compressor, when the system has a correct refrigerant fill you will rarely see high side pressures over 20 ATM - even at elevated temperatures.